The present invention relates to a floppy disk drive unit and, in particular, to apparatus for shifting the magnetic read/write head carriage in a floppy disk drive unit to align the magnetic heads with tracks on the disk.
Commercially available floppy disk drives comprise an assembly for holding and rotating a floppy disk and a separate assembly for holding and shifting the position of magnetic heads with respect to the rotating floppy fisk. In a conventional system, this latter assembly includes a carriage, moveable radially relative to the floppy disk such that the magnetic heads are positioned accurately with respect to tracks on the disk.
The U.S. Pat. No. 4,139,877 to Townsend discloses a magnetic read/write head carriage assembly which is shifted by means of a stepper motor and a coaxially connected "lead screw" which operates, upon rotation, to move the carriage, and the magnetic heads arranged thereon, in a direction radial to the center driven floppy disk. By controlling the increments of rotation of the stepper motor, the magnetic heads may be aligned to effect data transfer with selectable tracks on the disk.
As is conventional, the lead screw and stepper motor are provided with a total of three bearings: one on each side of the rotor in the stepper motor and a third at the end of the lead screw farthest from the stepper motor. This bearing arrangement requires either precise alignment, so that all three bearings are arranged along the common axis, or a universal joint at the point where the lead screw connects to the stepper motor rotor shaft.